This invention relates to pressure responsive capacitors having a pressure responsive diaphragm which comprises one capacitor plate and which cooperates with a thick film metallic coating which comprises a second capacitor plate. The invention more particularly relates to pressure responsive capacitors as described above where changes in capacity are due principally to pressure responsive changes in the effective area of the capacitor plate.
Pressure transducing or sensing devices of various types are well known in the art. Of these devices, types of pressure responsive capacitors have been devised wherein a pressure responsive diaphragm is sealed over an electrode fixed on a dielectric substrate so that changes in pressure difference across the diaphragm cause the distance between the diaphragm and fixed electrode to vary, thus varying the capacity between the diaphragm and fixed electrode in accordance with pressure. Such a device is described in U.S. Pat. No. 3,808,480. In the art, these pressure responsive capacitors have been arranged in frequency determining circuits or oscillators to provide a frequency signal correlated to pressure. It has also been suggested that the pressure responsive capacitors be arranged in bridge circuits to provide a voltage correlated to pressure.
Another type of known pressure responsive capacitor is comprised of a resilient dielectric material sandwiched between at least two electrode plates. Pressure across the plate resiliently compresses the dielectric to produce a capacity correlated to pressure. An example of this type device can be seen in U.S. Pat. No. 3,302,080.
In these known types of pressure responsive capacitors, the change in capacity brought about as a result of a change in pressure has been caused by the change in distance between the fixed electrode and the pressure responsive diaphragm which comprises the second electrode of the capacitor. The change in capacity over the pressure difference range has thus been relatively limited, especially where a relatively small pressure responsive capacitor is involved.